The new version of the site has been slow at loading the icons (wich are a Glyphicons web font) for buttons and when I check the Javascript console in Chrome (Ctrl+Shift+J) it shows the following error:

GET /fonts/glyphicons-halflings-regular.woff 404 (Not Found)

After much testing and Googling it turns out my old IIS server does not have Mime types registered for .woff files.

So I go in to the IIS console, click MIME Types icon and add .woff as application/octet-stream – problem solved!